The invention relates to a device for transporting a flexible strip along a guide provided with at least two conical pressure rollers whose apices face each other and which are rotatable about an axis at right angles to the transport direction of the strip. At least at the area of the pressure contact with the strip, the rollers are made of an elastically deformable material. The force exerted by one pressure roller on the strip differs from the force exerted by the other pressure roller on the strip.
In the "Hewlett-Packard Journal" of the December 1982, pages 29 and 30, a device is described of the kind mentioned in the opening paragraph, which is marketed under the tradename "7470 A Graphics Plotter". Although it is not apparent from the document how the various pressure forces of the pressure rollers are obtained, it can be ascertained that each of the pressure rollers of the marketed device is coupled with a rotatable lever loaded by a tensile spring. The force exerted by the two springs on the pressure rollers in a direction at right angles to the plane of the strip at the area of the pressure contact is different. This has the effect that the strip will directionally engage the guide and is at the same time held taut.
The known device has the disadvantage that, due to tolerances in the rigidity and the dimensions of the two springs, the difference in pressure force does not always have that value which is desirable for obtaining an optimum guidance (directional effect) and for holding the strip taut to the optimum.
European Patent Application No. 0102022 also discloses a device in which use is also made of a separate spring for each pressure roller. However, a difference in pressure force is not intentionally applied for obtaining a directional effect towards the guide. Such a directional effect may occur in this device unintentionally and incidentally due to spring tolerances. It will be appreciated that in such a case no directional effect of a predetermined strength is obtained. The known device is therefore solely intended to hold the strip taut.
Furthermore, U.S. Pat. No. 3,929,327 discloses a device in which a directional effect towards a guide is obtained by means of a single elastically deformable conical roller. In this case, there is no question of simultaneously directing and stretching the strip.